Mechanism of tetrahydroxy-1,4-quinone cytotoxicity: Involvement of Ca2 2+ and H 2O 2 in the impairment of DNA replication and mitochondrial function

Abstract

In this work we investigated the toxicity of a polyphenolic p-benzoquinone derivative, the tetrahydroxy-1,4-quinone (THQ) toward V79 Chinese hamster fibroblasts and analyzed the role of H202 and Ca 2+ in that mechanism. The exposure of exponentially growing cultures to THQ, in the presence of 1.0 mM Ca 2+, caused a dose-dependent inhibition of cell growth and DNA synthesis. Complete prevention of those effects by catalase indicated that H 20 2-induced damages should underlie both toxic processes. Further detection of a rise in the intracellular free Ca2 2+ concentration ([Ca 2+]i) in cells exposed to THQ plus Ca 2+ together with the partial protection conferred by the intracellular Ca 2+-chelator fura-2 against cell growth inhibition, indicated that a disruption of Ca 2+ homeostasis is a determinant event in THQ cytotoxicity. Furthermore, the intracellular accumulation of rhodizonic acid (RDZ), the primary oxidative product of THQ, indicated that THQ, or its corresponding semiquinone form, was entering the cells and undergoing further autoxidation to RDZ. It was also evidenced that mitochondria represent an important target in the development of THQ toxicity, as shown by the disruption of the transmembrane electrical potential (Δψ) of isolated rat liver mitochondria, as well as by the Ca 2+-release by mitochondria of permeabilized V79 cells. We concluded that disruption of Ca 2+ homeostasis and generation of H202 are critically involved in THQ-induced impairment of DNA replication and mitochondrial functions, leading ultimately to cell growth inhibition.